Is a party obligated to pay me for services provided if we agreed by word of mouth alone?

In most cases, oral agreements are as valid and enforceable as written ones.  Only certain agreements, for example agreements to sell real estate or which can't be performed within one year, are required to be in writing.  From the little you've written, there appears to be no reason why your oral agreement would not be valid.  However, if the other party disputes that there was an agreement, or what its terms were, you would have a much better chance of convincing a court that you were telling the truth if you had some documentation.  Even without an agreement, however, you may be able to collect for the fair market value (as opposed to the contractually agreed amount) of your services based on the legal theory of "quantum meruit".  Basically, while quantum meruit cannot supercede the terms of an express agreement, where for whatever reason there is no valid agreement, and you provide a benefit to another party with their consent, you are generally entitled to receive the fair value of your efforts as compensation.